Method of vaporizing mercury



Feb. 13, 1934. J. J. GREBE METHOD OF" VAPORIZING MERCURY Filed July 31.1930 2 Sheets-Sheet l 1 III] Fig. 2

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ATTORNEY Fig. 6

Feb. 13; 1934. J J, GREBE 1,946,851

METHOD OF VAPORIZING MERCURY Filed July 31. 1930 2 Sheets-Sheet 2INVENTOR ATTORNEY Patented Feb. 13, 1934 UNITED STATES METHOD OFVAPORIZING MERCURY John J. Grebe, Midland, Mich-., assignor to The DowChemical Company, Midland, Mich., a corporation of Michigan ApplicationJuly 31, 1930. Serial No. 472,026

Claims.

The present invention relates to methods for vaporizing mercury.

Many attempts have been made to vaporize mercury and use the vaporthereof, e. g., in a 5 power cycle, whereby it was anticipated thathigher economy would be realized in contrast with the use of steam alonefor this purpose. It has been attempted to vaporize the mercury byboiling same in metal tubes exposed to the heat of a furnace, to expandthe mercury in a turbine, to condense the expanded mercury vapor in heatexchange relation with boiling water, to utilize the steam so obtainedin a heat engine adapted to generate power therefrom and to return thecondensed mercury to the mercury boiler. Various diificulties have beenencountered and some overcome, but it still remains true that it is notyet practicable to boil a body of liquid mercury in a metal tube sincethe mercury does not wet such a tube, the heat transmission co-eficientis low and mercury has a pronounced tendency to bump, and further, thatthe amount of mercury required, even in the best installations as yetworked out, amounts to several pounds per kilowatt capacity. Thedifiiculty with boiling the mercury and the large investment perkilowatt in mercury constitutes heavy handicaps to an otherwiseattractive power cycle development.

I have invented a method of removing these two handicaps in a simple andeasily controlled manner.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the methods and means hereinafter fully described andparticularly pointed out in the claims, the annexed drawings and thefollowing description setting forth in detail several modes and meansfor carrying out the invention, such disclosed modes and meansillustrating, however, but several of various ways in which theprinciple of the invention may be used.

In order to vaporize mercury I take advantage of the well-knownphenomenon that if a liquid be introduced, preferably in the form ofspray, into superheated vapor thereof, the liquid will desuperheat thevapor and the superheat of the vapor will be converted into latent heator" evaporation of the liquid so introduced. I am thereby able toeliminate the boiling of a body of liquid mercury in contact with ametal surface and to construct a boiler which operates with very littlemercury. I accordingly vaporize the mercury by introducing it,preferably in the form of a fine spray, into superheated mercury vaporpreferably in the form of a current thereof, controlling the rate ofintroduction of the liquid mercury relative to the heat available in thesuperheat of the mercury vapor or otherwise available so that the liquidmercury so introduced will be either vaporized to substantialcompleteness, or suniciently so to satisfy the limitations of theparticular vaporizing equipment chosen for carrying out the step. I mayintroduce the liquid mercury into a current of presuperheated mercuryvapor in such amount as to substantially desuperheat the latter and alsosubstantially completely to vaporize the mercury introduced, or I mayintroduce the liquid mercury in excess, or again, I may introduce lessthan enough liquid mercury to fully desuperheat the vapor. I mayfurthermore, introduce the liquid mercury into a current of mercuryvapor while heating such vapor, that is, the mercury vapor may beabsorbing heat from a heat source at the same time that the liquidmercury is absorbing heat from the vapor.

Inasmuch as the latent heat requirement for evaporation is largerelative to the heat capacity of mercury vapor, even when considerablysuperheated, I may introduce the mercury to be vaporized in successiveportions into a current of mercury vapor subjected to indirect heatabsorbing relation with a source of heat, such as an extended tubularpassageway in a furnace, whereby the vaporization with superheat will bedone in successive stages. A variety of arrangements may be employed anda number of them are illustrated in the drawings.

In said drawings: Fig. 1 represents broadly in part section an apparatusfor introducing the mercury in the form of a spray into a current ofmercury vapor. Fig. 2 represents partly in cross section a vaporizer inwhich the mercury is introduced through a tube, the outer surface ofwhich is in contact with mercury vapor. Fig. 3 represents a crosssection of the simple form of vaporizer shown in Fig. 2. Figs. 4, 5, 6,'7, 8, and 11 represent diagrammatically a variety of evaporator hookupsadapted to carry out my invention.

Figs. 9 and 10 represent mod fications of Fig. 2.

Fig. 12 is a diagrammatic representation of an alternative method ofintroducing liquid mercury wherein excess is automatically returned tothe mercury feed pump.

Describing the above listed drawings in greater detail, Fig. 1illustrates a vapor pipe 1 intcwhich a smaller pipe 2 carrying a spraynozzle 3 is introduced, whereby a spray of liquid mercury may beinjected via pipe 2 and nozzle 3 into pipe 1. In Fig. 2 is illustrated aheating tube 1 into which a small tube 2 is inserted. If now heat beapplied to tube 1 and mercury injected through the fine bore tube 2, itwill be vaporized initially in tube 1. The vapor therein will, if therate of heating is suflicient relative to the rate of feed of liquidmercury, superheat the vapor therein, which superheated vapor will thentransmit heat to the mercury in tube 2 and an equilibrium condition maybe reached by proper control in which the mercury will be vaporizedentirely or largely in the fine bore tube 2 and the vapor thereof willbe superheated in tube 1, redelivering a part of of its heat to themercury in tube 2, finally issuing through the extension tube 1:0 to anyfurther point of use. A cross section of the tubes 1 and 2 is shown inFig. 3.

In Fig. 4 I show diagrammatically a turbine generator unit 5, acondenser 6, a boiler feed pump 7 and a furnace or heating zone 8. Insuch furnace I set the initial mercury preheater 9, together with aplurality of superheaters 1. One coil-type initial heater 9 and threecoil-type superheaters 1 are indicated. The pump 7 delivers the liquidmercury via pipe 2 to the initial heater 9 in which it is heated and mayeven be partially vaporized. The products of this step are then injectedinto a current of superheated mercury vapor through the aspirator orinjector 3, thereby acting to recirculate mercury vapor through thesuperheaters 1 via the headers la, lb, and 10, whereby a continuouscurrent of mercury vapor superheated in the heaters l is brought to theaspirator 3 and there mingled with mercury and distributed via theheader 1a to the heaters l. A branch vapor main 1a: conducts superheatedmercury vapor to the turbine.

Fig. 5 represents a modification of my vaporizer or boiler in which aninitial vaporizer coil 9 is followed by a series of superheater coils1a, 1b, 1c, 1d, 16. Liquid mercury from the condenser is delivered toeach of said coils via the pipe 2 through the T-valves 2a, whereby aportion is vaporized in 9 to furnish an initial current of vapor. Suchvapor is then superheated in la, whereupon an additional quantity ofmercury is injected and vaporized at 3a. The thus augmented mercuryvapor is again superheated in heater 11), after which an additionalportion of mercury is introduced at 3b, after which the still furtheraugmented mercury vapor current is again superheated and again augmentedin the following heaters and injectors until it is delivered assuperheated vapor through the pipe 13: leading to the turbine. Here noaspirating action of the injectors 3 is required, it being erelynecessary to supply the liquid mercury at a pressure sufficiently abovethe terminal vapor pressure desired to insure injection thereof at allpoints. The expansion of the mercury into vapor is here depended upon toset up the flow of vapor in the system.

A further modification of my mercury boiler is shown in Fig. 6 in whichthe recirculation of mercury vapor in the heater system is provided forby a booster pump 13, the liquid mercury being introduced via the supplypipe 2 at a plurality of points 3 in the flow of superheated vapor, aportion of which latter is withdrawn from pipe 1r by the pump 13 and isreturned to the heater system via pipe 1.

In Fig. '7 the liquid mercury is supplied through the pipe 2, a portionbeing introduced therefrom into an initial vaporizing coil 9 containedin a jacket 9a. This Jacket receives superheated mercury vapor from thepipe 1a, such superheated mercury vapor being produced by augmenting theportion vaporized in 9 by introduction of further liquid mercury intothe succeeding heaters, in which heaters such additional portions ofmercury are successively vaporized. The vapor leaving the jacket 9a isthen superheated in the final heater 1e for delivery to the turbine viapipe lac.

In Fig. 8 is shown still another modification having close relationshipwith that shown in Fig. '7. Here, instead of the jacket 9a about thecoil 9, a vapor pipe 9a surrounds initial vaporizing pipe 9. Suchconstruction may be as detailed in Figs. 9 and 10. In Fig. 9 mercury inthe small bore tube 9 is heated by the mercury vapor sur rounding same,which mercury vapor receives its heat from the furnace through the wallsof the outer pipe 9a. Fins or other extended configuration of thesurface of pipe 9 may be employed. In Fig. 10 a plurality of smallmercury vaporizing pipes 9 are shown as contained within the larger pipe9a.

It has been found that bumping may be overcome and the heat transferco-efficient between mercury and the wall of a heating tube greatlyincreased by passing liquid mercury at a high velocity over the heatingsurface. This is provided for automatically in the construction shown inFigs. 9 and 10 where small bore heating tubes are employed in which theformation of vapor imparts to the mercury a high velocity, giving it ascrubbing action, thereby absorbing the heat rapidly from the tube wall.Mercury vapor itself is dense and the rate of transmission of heatbetween the tube wall and vapor is high. It is therefore ideally suitedto take heat from the wall of the tube 9a and deliver it to the outersurface of the tubes 9.

In Fig. 11 is shown diagrammatically a more complete set-up of a turbinegenerator unit 5, a condenser water boiler 6, a boiler feed pump '7 anda vaporizer unit similar to that shown in Fig. 8. Such vaporizer unit aswell as others herein described may contain as many successive stages ofintroduction of mercury as required for the pressure and temperatureconditions employed. Instead of using the boiler indicated in Fig. 8 anyother type, including those previously described, may be employedprovided that mercury is therein vaporized in direct contact withsuperheated mercury vapor.

Fig. 12 represents diagrammatically a method of introducing liquidmercury into the vaporizing system at a number of points in such mannerthat any excess so introduced will be automatically returned to themercury feed pump.

In this figure the feed pump is indicated at 7, drawing mercury from thehot well 6 and delivering via the header 2 to a plurality of spraynozzles 3 in a tubular heating system 1. Under normal operation the sointroduced liquid merturn header lg to the trap 1h, in turn deliveringto the hot well 6 or pump 7. In this arrangement, as in the othersdescribed, the tubes into which the mercury is introduced may be in theheating zone so that vaporization of the mercury by desuperheating thevapor occurs accompanied by coincident heating of the mercury vaporwhereby a larger proportion of liquid mercury may be introduced at e chpoint of introduction,

thereby limiting the number of points of introh ing such excess liquidas provided for in Fig. 12 at outlets located between the inlets forliquid, the vapor will have an opportunity to acquire superheat beforereaching the next succeeding point of introduction, and, further, bysuch arrangement, necessity for close control is obviated since anexcess of liquid may be systematically introduced, separated andrecirculated. It should be noted that with this method of vaporizationnot only will the liquid mercury so introduced be vaporized by superheatof the vapor into which it is introduced, but it may absorb heat byradiation from the heating surface or by contact therewith, suchcontact, however, not being between a body of the mercury and theheating surface, but between a film of mercury and the heating surfacewhereby bumping is avoided. Where such a film does not actually contactwith the heating surface, it will be separated therefrom by a film ofvapor. Such film of vapor will be acquiring heat from the heatingsurface and delivering it to the mercury in contact therewith. Theseparated mercury at boiler temperature may be returned directly to thepump suction by the automatic trap lb or through a preheater or beotherwise reintroduced into the feed line 2.

In the control of my improved method of vaporization various proceduresmay be followed. One such procedure will involve control of the heatinput responsive to load, for example, responsive to the rate of flow ofvapor from the mercury boiler to the power mover through a flow meter,or responsive to the pressure of the vapor after the superheater orvaporizer system. The latter method of control will act to maintain aset pressure at the power mover. The supply of liquid mercury to theboiler will be controlled to keep a constant quantity of mercury in thesystem and may be made responsive to pressure in the vaporizing system,i. e. to supply more as the pressure rises and less as it falls. Themechanisms for such control are well understood and will not be hereindescribed.

A distinguishing feature of my improvements comprises the vaporizationof liquid mercury by direct contact with mercury vapor as heating agent,preferably by mingling with superheated vapor, liquid mercury preferablyin the form of a spray. In this manner I am able to eliminate thepresence of any consequential weight or vol ume of liquid mercury in thevaporizer, restricting such liquid mercury to the small amount in thecondenser, hot well, pump, and boiler feed lines. As a result, I am ableto reduce the mercury requirements of a power system of the characterdescribed to a fraction of a pound f inercury per kilowatt capacity, ahighly desirable advantage from the standpoint of initial costs ofmercury and a necessary condition if any large development in this fieldis to be made possible with a limited supply of available mercury. Ihave further obviated difficulties of bumping when boiling mercury in abody in contact with a heating surface, and, further, by reducing theweight of mercury in the system have correspondingly reduced theeconomic and other hazards following leakage or loss of the entiremercury charge through accident or faulty manipulation of equipment.

Although I have described various means for accomplishing thevaporization of mercury in accordance with my invention, it is obviousthat various other means and arrangements may be employed withoutdeparting from the spirit of the invention so long as liquid mercury isvaporized by contact with a current of superheated mercury vapor.

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the means andthe steps herein disclosed, provided those stated by any of thefollowing claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as myinvention:-

1. The method of vaporizing mercury which comprises causing a current ofmercury vapor to traverse a heating zone wherein the same is superheatedby transfer of heat from an external source and simultaneously injectinginto said current successive small portions of liquid mercury, wherebysuch liquid is vaporized by the superheat of the vapor.

2. The method of vaporizing mercury which comprises circulating acurrent of mercury vapor under superatmospheric pressure in a closedsystem, heating such vapor to superheat the same, simultaneouslyinjecting successive small portions of liquid mercury into said current,whereby to vaporize such liquid by the superheat of the vapor, andwithdrawing the vapor so generated for delivery to a point of use.

3. The method of vaporizing mercury which comprises preheating a body ofliquid mercury, injecting successive small portions of such preheatedliquid into a current of superheated mercury vapor undersuperatmospheric pressure, whereby to vaporize such liquid by thesuperheat of the vapor, simultaneously supplying heat from an externalsource to resuperheat the vapor, recirculating a portion of thesuperheated vapor for vaporizing additional liquid mercury andwithdrawing the balance of the vapor for delivery to a point of use.

4. The method of vaporizing mercury which comprises preheating a body ofliquid mercury, injecting successive small portions of such preheatedliquid into a current of superheated mercury vapor undersuperatmospheric pressure, whereby to vaporize at least the major partof such liquid, tapping on unvaporized liquid and returning the same tothe supply source for liquid mercury, supplying heat to said vaporcurrent to resuperheat the vapor, recirculating a portion of thesuperheated vapor for vaporizing additional liquid mercury andwithdrawing the balance of the vapor for delivery to a point of use.

5. The method of vaporizing mercury which comprises preheating a body ofliquid mercury, injecting successive small portions of such preheatedliquid into a current of superheated mercury vapor undersuperatmospheric pressure, whereby to vaporize at least a major part ofsuch liquid, removing unvaporized liquid mercury, supplying heat to saidvapor current to resuperheat the vapor, recirculating a portion of thesuper-- heated vapor for vaporizing additional liquid mercury andwithdrawing the balance of the vapor for delivery to a point of use.

JOHN J. GREBE.

